Threaded insert made of wire

ABSTRACT

The invention relates to a wire-type screw thread insert for insertion into a tapped hole of a workpiece. A cylindrical body comprising a plurality of helically wound coils is provided with at least one insertion zone which is bent radially inwards from the outer diameter of the cylindrical body and extends about a circumferential angle of about 360° to 720°. This facilitates insertion of the insert into a tapped hole of the workpiece so that special tools required hitherto may be dispensed with because the wire-type screw thread insert of the invention may be readily introduced into the tapped hole and may be threaded thereinto by a simple tool.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a wire-type screw thread insert for insertioninto a tapped hole of a workpiece consisting of a cylindrical bodycomprising a plurality of helically wound coils and an end coil whichextends radially inwardly from the outer diameter of the cylindricalbody and a use of such a wire-type screw insert in a tapped hole of aworkpiece.

2. Description of the Related Art

Such wire-type screw thread inserts have become known, e.g. from U.S.Pat. No. 2,363,789, EP-A-140 812 and EP-A-157 715. Generally, the outerdiameter of the cylindrical body is to be designed so as to exceed theouter diameter of the tapped hole in the workpiece so that the diameterof the wire coils is to be reduced when the insert is threaded into thetapped hole of the workpiece in order to provide for a tight grip of thescrew thread coils in the tapped hole by resilient deformation of thewire coils. In order to facilitate threading of the wire-type screwthread insert into the tapped hole, half a coil at the end of thecylindrical body is deformed radially inwards in a manner known per se(EP-B1-0 228 981). The minimal outer diameter of the radially deformedportion should be substantially as large as or slightly larger than theassociated outer diameter of the tapped hole. Furthermore, with thisprior art wire-type screw thread insert the cross-section of the wire atthe end thereof is reduced in a predetermined manner in order tofacilitate insertion thereof and to avoid damaging the tapped hole.According to U.S. Pat. No. 2,152,681 the outer diameter of the reducedend portion is somewhat smaller than the outer diameter of the tappedhole. The circumferential angle of the reduced diameter portion again is180°. A similar wire-type screw thread insert has become known from U.S.Pat. No. 2,371,674 wherein, as may be seen in FIGS. 1 and 2 of thatdocument, the end coil extends, following its diameter reducing portion,through a small angular range about a circumferential angle of somewhatmore than 180°.

SUMMARY OF THE INVENTION

Nevertheless it is necessary with the prior art wire-type inserts to usea special tool comprising a preclamping cartridge and a spindle to beinserted initially into the wire-type screw thread insert in order toreduce the diameter of the insert before it is threaded into the tappedhole. Such an insertion tool has been described for example in U.S. Pat.No. 4,553,302. While it is possible to reduce the outer diameter inorder to facilitate the threading operation, this however will weakenthe tight grip, or specific regulations will not be met.

The problem to be solved by the invention is to design the wire-typethread insert such that insertion thereof into the tapped hole will befacilitated and in particular may be performed without a tool forreducing the diameter of the wire-type screw thread insert beforeinsertion thereof

This problem is solved by the features of patent claim 1. Advantageousmodifications thereof are defined in the subclaims.

In contrast to prior art wire-type screw thread inserts the inventionprovides for an insertion area consisting of the end coil (of a reducedand constant outer diameter) and the diameter reducing portion whichtogether extend about a circumferential angle of preferably about 360°and more. Even a circumferential angle of about 360° facilitatessubstantially the insertion operation and above all allows to dispensewith the so-called preclamping cartridge for reducing the outer diameterof the wire-type screw thread insert before insertion thereof. Thisallows to substantially simplify the insertion tool. The end coil withthe reduced and constant outer diameter is concentric to the cylindricalbody so that the wire-type screw thread inserts will not be misalignedwhen the insertion tool will be applied. This facilitates insertion ofthe insert into the tapped hole of the workpiece. Furthermore, the endcoil is slightly overdimensioned with the reduced outer diameter of thefinal coil exceeding the outer diameter of the tapped hole, preferablyfor 0.1 mm. This enables manual insertion of the end coil into thetapped hole. Overdimensioning of the end coil ensures that the end coildoes not extend radially inwards too far so as to interfere with thebolt being screwed into the insert.

When the cylindrical body of the insert has been inserted into thetapped hole, further threading-in of the insert is performed by a simpletool for reducing the outer diameter of the cylindrical body. The toolfor example may be a dimensionally mating screwdriver. For engagement ofthe tool either the wire-type screw thread insert is provided with atang which is broken off and removed after the insertion operation, orthe tool has a nose engaging into a recess of the end coil. An insertionzone designed in accordance with the invention preferably is provided ateach end of the wire-type screw thread insert so that no directionalorientation of the insert is required for the insertion operation, whichwould be required when only one end of the insert would be designed inaccordance with the invention.

In a manner known per se the length of the screw thread insert beforeinsertion into the tapped hole is somewhat less than after insertionthereof. As a result the pitch angles of the wire-type screw threadinsert before assembly are somewhat less than after assembly. Withwire-type screw thread inserts of very small pitch angles the inventionprovides for the insertion zone to extend about a circumferential angleof more than 360°. Preferably, a full intermediate coil will be providedbetween the end coil and the cylindrical body, with the intermediatecoil having an outer diameter between the constant diameter of the endcoil and the diameter of the cylindrical body. As a result the end coilwill be supported at the insertion tool and cannot move radially inwardsso as to enter the interior of the wire-type screw thread insert

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will be explained in more detail withreference to the drawing. In the drawing:

FIG. 1 is an end view of a wire-type screw thread insert having a tang,

FIG. 2 is a longitudinal section of the wire-type screw thread insert inFIG. 1,

FIGS. 3 and 6 are longitudinal cross-sections of the tapped hole in theworkpiece.

FIG. 4 is an end view of a wire-type screw thread insert having a driverecess, and

FIG. 5 is a longitudinal section at an enlarged scale of an insertionzone at the end of a wire-type screw thread insert Which has anintermediate coil.

DETAILED DESCRIPTION OF THE INVENTION

The wire-type screw thread insert 10 as shown n FIGS. 1 and 2 is to bethreaded into a tapped hole of an outer diameter D in a workpiece 12according to FIG. 3.

In a manner known per se the wire-type screw thread insert 10 consistsof a plurality of individual coils which are wound to form a cylindricalbody of an outer diameter d which somewhat exceeds the tapped holediameter D and which is dependent on whether the threads of the tappedhole are of a standard pitch type R or a fine pitch type F. When thethreads are of the standard pitch type, the outer diameter D_(R) of thescrew thread insert equals the product of the outer diameter D of thetapped hole and the factor 1.05. When the threads are of the fine pitchtype the outer diameter d_(F) of the screw thread insert 10 equals theproduct of the outer diameter D and the factor 1.08.

FIGS. 1 to 4 furthermore show an insertion zone extending for a fullconvolution of about 360°, i.e. it is of a reduced outer diameter d₁ formore than 180°. This may be recognized in particular in the end view ofFIG. 1 where the end coil 15 follows a diameter reducing portion between16 and 17 so that the insertion zone extends about a full convolution,i.e. for about 360°. In the insertion zone the coils are bent radiallyinwards from the outer diameter d of the cylindrical body at 16 untilthe reduced outer diameter d₁ of the end coil 15 is reached at the point17 after a circumferential angle of about 90°. Thereafter, the reducedouter diameter d₁ will be constant for more than a circumferential angleof 180°, preferably for about 270°, so that an insertion zone of about360° will result. This facilitates insertion of the insert into thetapped hole and assists to maintain the wire-type screw thread insertconcentrically aligned. The outer diameter d₁ equals the hole diameter Dplus 0.1 mm.

In the area between the desired break point 20 and the end 18 of the endcoil 15 where the end coil arcuately merges into the radial part of thetang 19, the outer diameter is still further reduced so that there willbe a transition to the radial portion of the tang 19. This additionaldiameter reduction will not interfere with a bolt being screwed into thewire-type screw thread insert engaged in the tapped hole 11, because thetang 19 will be cut off at the desired break point 20.

FIG. 4 shows a wire-type screw thread insert which in a manner known perse is provided with a drive recess 21 which may be engaged by a pawl ofa not shown insertion tool in order to thread the insert into the tappedhole. The forward end 22 of the end coil 15 is slightly truncated as isknown per se. Otherwise, the end coil 15 and the diameter reducingportion 16, 17 together of about 360° are designed in the manner asexplained with reference to FIG. 1 so that the screw thread insert maybe inserted into the tapped hole by rotating it manually until theportion of the end coil 15 diametrically opposite to the insertion endthereof will engage the tapped hole in the workpiece so that the insertwill have been inserted into the tapped hole whereupon further threadingof the insert into the tapped hole is performed by a suitable tool whichengages the recess 21.

Even though this has not been shown in the drawing, it goes withoutsaying that the other end of the cylindrical body may also be providedwith a similar end coil 15.

FIG. 5 is a section of an end of a wire-type screw thread insert 10'having an insertion zone consisting of an end coil 15 of an outerdiameter d₁ and an intermediate coil 23 of an outer diameter d_(F1) whenthe threads are of the fine pitch type F. The screw thread insert is ofan outer diameter d_(F). Furthermore, the pitch anlge α of the coilsafter assembly thereof is indicated. The intermediate coil 23 may alsobe a complete coil of about 360° so that altogether the circumferentialangle of the insertion zone including the end coil 15 and theintermediate coil 23 will be about 720° corresponding to an end coil 15of about 270° plus the diameter reducing portion through theintermediate coil 23 of about 450° as shown in FIG. 5. This ensures thatthe coils of the insertion zone can engage each other during assembly.

The following relationships for standard pitch threads and fine pitchthreads will result:

outer diameter d₁ of the end coil=D of the tapped hole plus 0.1 mm.

For fine pitch threads: outer diameter d_(F1) of the intermediate coil23=D×1,05, outer diameter d_(F) of the cylindrical body=D×1.08.

If an intermediate coil 23 is required for threads of the standard pitchtype, the respective relationships are as follows: outer diameter d_(R1)of the intermediate coil 23=D×1.03, outer diameter d_(R) of thecylindrical body=D×1.05.

What is claimed is:
 1. A wire-type screw thread insert for a tapped holeof a workpiece, said tapped hole have a plurality of threads and saidwire-type screw thread insert consisting of a plurality of coilshelically wound about a central axis and comprising a cylindrical mainsection and at least one end section, said cylindrical main sectionhaving a first outer diameter and the threads of said tapped hole havinga tapped hole outer diameter which is smaller than said first outerdiameter by a predetermined amount, said at least one end sectionconsisting of a terminal end portion having a uniform second outerdiameter and an intermediate end portion having an outer diameterdecreasing from said first outer diameter to said second outer diameter,said tapped hole outer diameter beina smaller than said second outerdiameter, said end section extending for 360° to 720° about said centralaxis and said terminal end portion extending for at least 180° aboutsaid central axis, said end section including drive means for engagementof a tool for threading the wire-type screw thread insert into saidtapped hole.
 2. A wire-type screw thread insert as defined in claim 1wherein said terminal end portion extends for 270° and said intermediateend portion extends for 450°.
 3. A wire-type screw thread insert asdefined in claim 1 wherein said first outer diameter of said cylindricalmain section equals said tapped hole outer diameter times 1.05 when thethreads of said tapped hole are of a standard pitch type.
 4. A wire-typescrew thread insert as defined in claim 1 wherein said first outerdiameter of said cylindrical main section equals said tapped hole outerdiameter times 1.08 when the threads of said tapped hole are of a finepitch type.
 5. A wire-type screw thread insert as defined in claim 2wherein an average outer diameter of said intermediate end portionequals said tapped hole outer diameter times 1.03 when the threads ofsaid tapped hole are of a standard pitch type.
 6. A wire-type screwthread insert as defined in claim 2 wherein an average outer diameter ofsaid intermediate end portion equals said tapped hole outer diametertimes 1.05 when the threads of such tapped hole are of a fine pitchtype.
 7. A wire-type screw thread insert as defamed in claim 1 whereinsaid second outer diameter of said terminal end portion equals saidtapped hole outer diameter plus 0.1 mm.